Non-associative learning processes in vestibular nucleus.

Simple non-associative learning processes, habituation and sensitization, are known to be systemically involved in different neurotransmissions, and these processes in the vestibular nucleus (VN) often show opposite responding patterns to repeated stimuli. However, their roles and mechanisms of the reciprocal responses at the cellular level are still elusive. Here, we conducted an electrophysiological experiment to investigate the neuronal responses to repeated stimuli in the VN, characterizing the neuronal responding patterns of habituation and sensitization. Based on our results, we also suggested an alternative hypothesis that these non-associative neuronal responses generated biased neural information based on simple linear addition. Sixty-seven neuronal responses to repeated stimuli were recorded from 23 guinea pigs, and the habituated and the sensitized responses were 37 (range of slopes - 3.66~- 0.02 spks/s/trial) and 30 (0.01~1.51 spks/s/trial), respectively. Unlike previous study, the general neuronal responding shapes were not exponential, but most (94%, 63/67) responding profiles were linear. Although no strong relation between the irregular and the high sensitivity in our population, the neuronal irregularity and sensitivity could be the core factors to cause the biased results to more habituated side. In conclusion, we found that a biased neural response (mean ± STD - 0.22 ± 0.89 spks/s/trial) was constructed by two non-associative neuronal responses based on a linear addition of the slopes. Graphical abstract Hypothesized and calculated neural mediation by non-associative learning processes.